Nothing is as easy as it seems at first glance. A simple 8 bit add is making my day worse.

Problem is explained in this electric stackexchange question I opened: https://electronics.stackexchange.com/questions/312354/74181-alu-not-working-properly-cascaded-to-add-8-bit-numbers/

As a fun note, I just discovered that the standard Windows 7 calc has a very useful programmer mode, which makes life a lot easier while I haven't finished the Assembler program.